lesson from retail building operations

One of the major issues I’ve noticed while handling several retail stores is that BMS alarm systems are often programmed in a way that creates more confusion than clarity.

On paper, alarms are meant to help operators quickly detect problems, in reality, poorly structured alarm logic often does the opposite.

I remember one situation where a plant issue triggered what looked like a storm of alarms across the building.

Within minutes we had alarms coming from:

• VAV boxes
• AHUs
• supply air temperature
• zone temperature
• airflow failures

The operator screen was full. It looked like the entire building was failing.

But when we started digging into the issue, the real cause turned out to be a single upstream failure in the cooling plant.

Everything else was simply a symptom propagating downstream.

Why this happens

Most HVAC systems are hierarchical by nature. A typical cooling chain looks like this:

Cooling Tower → Chiller → CHW Pumps → AHU → VAV → Zone

If something goes wrong at the top of this chain, the effects naturally propagate downward.

For example:

If the chiller plant stops producing chilled water, then:

• AHUs will show high supply air temperature
• VAV boxes will show low airflow or temperature alarms
• Zones will show high room temperature

The BMS may display dozens or even hundreds of alarms, even though the actual root cause is only one fault.

This creates a major operational problem.

Instead of helping operators respond quickly, the alarm system floods them with symptoms, forcing them to waste time investigating equipment that is actually working correctly.

The concept of Hierarchical Alarm Suppression

A much smarter approach is described in ASHRAE Guideline 36 — High-Performance Sequences of Operation for HVAC Systems.

The guideline introduces a concept called: Hierarchical Alarm Suppression.

The idea is simple but powerful.

Equipment in HVAC systems can be classified as either:

• Source — equipment that provides resources
• Load — equipment that depends on those resources

For example:

• Chiller → source of chilled water
• AHU → load to the chiller
• VAV box → load to the AHU

If the source system fails, the alarms generated by the downstream loads are suppressed, because they are not the real problem.

Instead, the operator sees the root alarm.

What this looks like in practice

Consider a building with:

• 2 chillers
• 6 AHUs
• 120 VAV boxes

If the chiller plant fails:

Without hierarchical alarm logic, the BMS might generate:

• multiple AHU alarms
• airflow alarms at VAV level
• dozens of zone temperature alarms

In some systems this can easily exceed 100 alarms.

With hierarchical suppression implemented correctly, the BMS instead highlights:

“Chiller Plant Failure”

The downstream alarms are temporarily suppressed because they are simply consequences of that event.

This dramatically improves the operator’s ability to diagnose the problem quickly.

Why this matters in real buildings

In retail environments where multiple stores depend on centralized HVAC systems, response time matters.

When operators face alarm flooding, two things usually happen:

1- They spend valuable time chasing symptoms
2- Eventually they begin to ignore alarms altogether

Both outcomes are dangerous for building operation.

A properly structured alarm hierarchy ensures that the system points directly to the root cause, allowing maintenance teams to act faster and more effectively.

A note on standards

The concept described above is documented in: ASHRAE Guideline 36 — Section 5.1.19 (Hierarchical Alarm Suppression)

This guideline provides a structured framework for defining relationships between HVAC systems (source, load, and system groups) and implementing intelligent alarm logic in building automation systems.

While many modern control sequences reference this approach, it is still rarely implemented properly in real projects.

Final thought

Good HVAC design is not only about loads, ducts, and equipment sizing.

It is also about how systems behave when things go wrong.

And sometimes the difference between a chaotic control room and a well-managed building comes down to something as simple as how alarms are structured.

f you are involved in HVAC operations or BMS programming, I would be interested to hear:

Have you experienced alarm flooding in your buildings?